As is well known, the manufacturing process of various kinds of electronic or semiconductor devices such as ICs, LSIs and the like involves fine patterning of a resist layer on the surface of a substrate material such as a semiconductor silicon wafer. This fine patterning process has traditionally been conducted by the photolithographic method in which the substrate surface is uniformly coated with a positive or negative tone photosensitive composition to form a thin layer and selectively irradiating with actinic rays (such as ultraviolet (UV), deep UV, vacuum UV, extreme UV, x-rays, electron beams and ion beams) via a transmission or reflecting mask followed by a development treatment to selectively dissolve away the coated photosensitive layer in the areas exposed or unexposed, respectively, to the actinic rays leaving a patterned resist layer on the substrate surface. The patterned resist layer, thus obtained, may be utilized as a mask in the subsequent treatment on the substrate surface such as etching. The fabrication of structure with dimensions of the order of nanometers is an area of considerable interest since it enables the realization of electronic and optical devices which exploit novel phenomena such as quantum confinement effects and also allows greater component packing density. As a result, the resist pattern is required to have an ever increasing fineness which can be accomplished by using actinic rays having a shorter wavelength than the conventional ultraviolet light. Accordingly, it is now the case that, in place of the conventional ultraviolet light, electron beams (e-beams), excimer laser beams, EUV, BEUV and X-rays are used as the short wavelength actinic rays. Needless to say the minimum size obtainable is, in part, determined by the performance of the resist material and, in part, the wavelength of the actinic rays. Various materials have been proposed as suitable resist materials. For example, in the case of negative tone resists based on polymer crosslinking, there is an inherent resolution limit of about 10 nm, which is the approximate radius of a single polymer molecule.
It is also known to apply a technique called “chemical amplification” to resist materials. A chemically amplified resist material is generally a multi-component formulation in which there is a matrix material, frequently a main polymeric component, such as a polyhydroxystyrene (PHOST) resin protected by acid labile groups and a photo acid generator (PAG), as well as one or more additional components which impart desired properties to the resist. The matrix material contributes toward properties such as etching resistance and mechanical stability. By definition, the chemical amplification occurs through a catalytic process involving the PAG, which results in a single irradiation event causing the transformation of multiple resist molecules. The acid produced by the PAG reacts catalytically with the polymer to cause it to lose a functional group or, alternatively, cause a crosslinking event. The speed of the reaction can be driven, for example, by heating the resist film. In this way the sensitivity of the material to actinic radiation is greatly increased, as small numbers of irradiation events give rise to a large number of solubility changing events. As noted above, chemically amplified resists may be either positive or negative working.
Certain chemically amplified resists do not use large polymers. In cases where nanometer-scale patterning is desired, low molecular weight polymers or even small molecules may be used as the resist matrix material. These are sometimes referred to as “molecular glass” resists (MGRs), taken in this instance to include molecules such as oligomers, polyaromatic hydrocarbon derivatives, discotic liquids crystals, fullerenes, macrocycles, small amorphous, and other low molecular weight resists. Although MGRs may offer many potential advantages over polymeric chemically amplified resists, there are still some things about this class of materials that could potentially pose challenges. Removal and subsequent volatilization of protecting groups in positive tone molecular resists may cause a loss of up to approximately 50% of the mass of the resist, potentially leading to a loss of pattern quality. The small sizes of molecular resist compounds, and often correspondingly low glass transition temperatures, can also restore material integrity but may compromise pattern quality.
Accordingly, there is a need for improved negative molecular glass resists. It is to the provision and characterization of such molecular glass resists that the various embodiments of the present written description are directed.